Hi, Folks just bought a sapphire 5850 and im overclocking it, im currently sitting at core 1000mhz memory 1100 ive done a stability test useing furmark for 20 mins temps are 68c at 70% fan speed could i push further ? which is more important to overclock core or mem ? any help would be appreciated cheers.

Core is most important. Have a look at some other 5850 threads to see what they are using for voltage. With 70% fan and 68c you are reaching the thermal limits of the cooler. Testing how far you can take the memory is easy. If you overclock it too much you will just notice a decrease in performance as it will automatically throttle the bandwith (for the lack of a better term.)